Fossil fuels remain an important source of energy in America and around the world. For example, natural gas is used to produce energy, to include heat and electricity, in commercial and residential settings. These resources are also components of numerous products used daily. For example, oil is a component in plastics, fuels, toiletries, cleaning products, clothing, and health products, among many others. Supplies of oil and natural gas, however, are finite. There is also a growing interest in many countries towards producing more of their own oil and natural gas resources in order to reduce or end dependency on foreign supplies. Thus, it is important for oil and natural gas recovery operations to responsibly optimize their productions of these resources.
One way to optimize gas and oil production is to utilize a hydraulic fracturing process. Hydraulic fracturing, or “fracking,” utilizes high pressure sand and water mixtures to restore flow rates of oil and natural gas in mining operations. In hydraulic fracturing, the high pressure mixtures are injected into to oil and gas wells. The high pressure contact between the mixture and the rock forms cracks in the rock containing the resource being mined. This, in turn, allows more of the resources in the rock to flow to locations in the well where they may be recovered. In the United States, hydraulic fracturing has resulted in the recovery of billions of barrels of additional oil and trillions of cubic feet of additional natural gas.
Water is a crucial part of the hydraulic fracturing process. In the United States, a hydraulic fracturing operation for a single well utilizes more than 5 million gallons of water. In order to preserve water resources, there is a strong interest in recycling water already present in mining operations, such as produced water. Produced water is water that is naturally present in oil and natural gas reservoirs and is extracted or co-extracted during recovery operations. As will be discussed later, hydraulic fracking used to recover natural gas produces what is sometimes referred to as frac flowback or frac water, which is an example of produced water. Recycling produced water, instead of using new water in hydraulic fracturing, leads to environmental and operational benefits. For example, recycling produced water for use in hydraulic fracturing may preserve water resources, especially in areas where there is little natural water. Recycling produced water also saves expenses related to shipping water to the drilling site, a consideration that is especially sensitive when drilling occurs in areas that are remote. Also, there is a potential reduction in frac water treatment chemicals, such as scale inhibitors, currently used in the industry.
One barrier to recycling produced water for use in hydraulic fracturing is that produced water contains high concentrations of scale forming constituents, such as calcium, barium, strontium, and magnesium. For example, a typical Marcellus Shale produced water would include approximately 10,600 mg/l of calcium, 10,100 mg/l of barium, 3,500 mg/l of strontium, and 973 mg/l of magnesium. These high concentrations should be reduced by at least 80% so that the produced water could be used in hydraulic fracturing without significant scaling. As such, there is a need for an efficient process to treat produced water to reduce the scaling potential thereof so that it may be recycled and utilized in hydraulic fracturing operations.